1. Technical Field
The present invention relates to wireless communications, and more particularly, to a method of transmitting uplink control signals in a wireless communication system.
2. Background Art
In order to maximize efficiency of a limited radio resource in a wideband wireless communication system, methods for more effectively transmitting data in time, spatial, and frequency domains have been provided.
Orthogonal frequency division multiplexing (OFDM) uses a plurality of orthogonal subcarriers. Further, the OFDM uses an orthogonality between inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT). A transmitter transmits data by performing IFFT. A receiver restores original data by performing FFT on a received signal. The transmitter uses IFFT to combine the plurality of subcarriers, and the receiver uses FFT to split the plurality of subcarriers. According to the OFDM, complexity of the receiver can be reduced in a frequency selective fading environment of a broadband channel, and spectral efficiency can be increased when selective scheduling is performed in a frequency domain by using a channel characteristic which is different from one subcarrier to another. Orthogonal frequency division multiple access (OFDMA) is an OFDM-based multiple access scheme. According to the OFDMA, efficiency of radio resources can be increased by allocating different subcarriers to multiple users.
To maximize efficiency in the spatial domain, the OFDM/OFDMA-based system uses a multiple-antenna technique which is used as a suitable technique for high-speed multimedia data transmission by generating a plurality of time/frequency domains in the spatial domain. The OFDM/OFDMA-based system also uses a channel coding scheme for effective use of resources in the time domain, a scheduling scheme which uses a channel selective characteristic of a plurality of users, a hybrid automatic repeat request (HARD) scheme suitable for packet data transmission, etc.
In order to implement various transmission or reception methods to achieve high-speed packet transmission, transmission of a control signal on the time, spatial, and frequency domains is an essential and indispensable factor. A channel for transmitting the control signal is referred to as a control channel. An uplink control signal may be various such as an acknowledgement (ACK)/negative-acknowledgement (NACK) signal as a response for downlink data transmission, a channel quality indicator (CQI) indicating downlink channel quality, a precoding matrix index (PMI), a rank indicator (RI), etc.
One example of the uplink control signal is a scheduling request. The scheduling request is used when a user equipment (UE) requests a base station (BS) to allocate an uplink radio resource. The scheduling request is a sort of preliminary information exchange for data exchange. In order for the UE to transmit uplink data to the BS, radio resource allocation is first requested by using the scheduling request. When the BS allocates the uplink radio resource in response to the scheduling request, the UE transmits the uplink data by using the allocated radio resource.
Compatibility with another control channel for transmitting another control signal has to be taken into consideration when the scheduling request needs to be transmitted on an uplink control channel. UE capacity capable of transmitting the scheduling request has to be also taken into consideration. A case where the scheduling request is transmitted simultaneously with other control signals has to be also taken into consideration. For example, the scheduling request and ACK/NACK signals may be simultaneously transmitted by one UE.
Accordingly, there is a need for a control channel having an effective structure for simultaneously transmitting a scheduling request and other control signals.